This invention pertains generally to apparatus and a method for increasing efficiency and/or decreasing exhaust emissions of an internal combustion engine.
The concern over air pollution and the dwindling of petroleum resources has resulted in legislation which has caused a shift in emphasis from powerful, high compression engines to small, low compression ones. As the degree of pollution which an automobile introduces into the air is measured in parts per mile, a smaller, lower compression engine, burning a leaner mixture (i.e., a higher ratio of air to fuel) can more readily satisfy the pollution requirements.
It is known on the one hand that the level of CO (carbon monoxide) produced by the internal combustion engine decreases as the air-fuel ratio is increased, and continues to decrease beyond the "chemically ideal" ratio of 14.7, and the decrease extends to the "lean limit", i.e., the limit at which flame speed drops to zero and at which the air-fuel mixture does not ordinarily ignite. The production of NO.sub.x (oxides of nitrogen), on the other hand, is most sensitive to the time at which the spark is fired (given in degrees before top dead center, BTDC). The production of NO.sub.x is parts per mile, jumps from approximately 1,000 to 3,000 parts when the spark timing is advanced over a 20.degree. range. In order to reduce carbon monoxide, oxides of nitrogen and also other hydrocarbons, therefore, one must operate the internal combustion engine with an air-fuel ratio lying at the lean end of the scale, and ignite the mixture as close to TDC as possible. The difficulties associated with these conditions are two-fold: firstly, as the mixture is made leaner, it will become increasingly more difficult to ignite with the spark, since the spark constitutes a constant external energy source of approximately 0.1 joule/spark energy capacity, and secondly, the resultant drop in flame speed along with spark timing near TDC will result in late combustion of the mixture and hence reduced efficiency as well as increased discharge of unburnt hydrocarbons through the exhaust. (On the other hand it is known that in order to increase engine efficiency as well as decrease exhaust emissions it is very desirable to ignite and sustain combustion of a lean mixture in an internal combustion engine.)
Among the prior art references are references teaching the utilization of microwave energy to study piston motion and combustion processes in piston-type internal combustion engines. Examples of such prior art references are Merlo U.S. Pat. No. 3,589,177 and Merlo U.S. Pat. No. 3,703,825. These references, however, are concerned with obtaining resonances in an engine cylinder between the engine cylinder head, cylinder wall, and the piston face so that the motion of the piston and the constituents of the cylinder can be analyzed. Since these references have a diagnostic procedure as their object, it will be appreciated that very low power microwave energy is employed in order to not substantially perturb the system under study.
In view of the foregoing it is a principal object of the present invention to provide a system which increases the efficiency, and also reduces the exhaust emissions of an internal combustion engine, which can be installed in existing internal combustion engines, with a minimum of engine modification, and is relatively cheap and easy to manufacture and install, and requires relatively low power in operation.
Other objects are to enhance combustion and increase flame speed in the combustion chambers of internal combustion engines and to provide an improved ignition support system for an internal combustion engine.
Other objects and advantages of the invention will become apparent from the following description of particular preferred embodiments of the invention when read in conjunction with the accompanying drawings.